1. Make beans: Cover beans with cold water by 2 inches in a bowl. Refrigerate 8 to 12 hours. Drain. Bring 8 cups water to a boil in large saucepan. Add beans, onion, and bay leaf. Reduce heat; simmer until beans are just tender, about 1 hour. Drain, reserving beans and 4 cups liquid. Discard solids from beans, and cover beans.

2. Make soffritto: Heat oil in a stockpot over medium-low heat. Add celery, carrot, and onion. Cook, stirring often, until deep golden brown, 20 to 25 minutes.

3. Make soup: Add leek and garlic. Cook, stirring often, until soft, about 4 minutes. Raise heat to medium-high; add celery, carrots, potatoes, zucchini, and green beans. Cook, stirring often, until golden, about 5 minutes. Stir in reserved bean liquid, the tomatoes and juice, kale, cabbage, stock, cheese rind, and red-pepper flakes; season with salt and pepper. Bring to a boil. Reduce heat. Cover; simmer 1 hour.

4. Add beans. Cover; cook until tender, 1 to 1 1/2 hours. Serve topped with pesto if desired. Minestrone can be refrigerated in an airtight container up to 3 days; thin with water if needed before reheating.